With the progress of aging of the society, number of patients suffering from dementia is ever more increasing. Dementia is the condition in which acquired intelligence has persistently declined by organic disorder of brain. Dementia has been classified into several types based on the pathogenesis and histopathology, and the most typical types are Alzheimer-type dementia and cerebrovascular dementia. Conceivably, these two types of dementia and the mixed type of these two constitute 80 to 90% of the entire dementia case.
Alzheimer-type dementia is associated with atrophy of brain, and up to this moment, no drug has been found that can fundamentally treat this disease. The only commercially available pharmaceutical product with the indication for Alzheimer-type dementia is donepezil hydrochloride (trade name Aricept: manufactured by Eisai Co., Ltd.). This product, however, is indicated for “inhibition of the advance of dementia symptoms of slight or moderate Alzheimer-type dementia”, and this product may not be sufficient in view of fundamental treatment of the disease.
Icosapentaenoic acid (also referred to as eicosapentaenoic acid, hereinafter abbreviated as EPA) which is a member of ω-3 polyunsaturated fatty acids is a polyunsaturated fatty acid extracted and purified from fish oil, and EPA is known for its effect of reducing serum lipids, suppressing platelet aggregation, and the like. In Japan, ethyl ester of this EPA is commercially available as a therapeutic drug for arteriosclerosis obliterans and a therapeutic drug for hyperlipidemia. EPA has been reported to retard advance of symptoms of Alzheimer-type dementia (see, for example, Non-patent document 1). This document discloses that, when the patients suffering from Alzheimer-type dementia were administered with EPA at a daily dose of 900 mg for 12 months, and the symptoms were observed (number of the evaluated case: 22), “administration of EPA to the patients of Alzheimer-type dementia resulted in the improvement of the cognitive skill for 3 to 6 months. However, after this period, the cognitive skill declined with the natural prognosis of the disease” (page 27, right column).
This document, however, does not disclose or indicate excellent effects on the Alzheimer-type dementia achieved by the combination of the ω-3 polyunsaturated fatty acid and thyroid hormone.
[Non-Patent Document]    Dementia Japan, 2001, vol. 15, pp. 21-29.